This invention concerns a polyester resin composition and a molding product thereof and, more in particular, it relates to a polyester resin composition excellent in chemical resistance, particularly, resistance to alkaline solutions and also excellent in mechanical strength, and a molding product formed by metal insert molding of the resin composition.
Since, thermoplastic polyester resins, among all, polybutylene terephthalate resins have properties suitable as engineering plastics such as excellent heat resistance, moldability, chemical resistance and electric insulation property, they have been used mainly for injection molding in application uses such as various kinds of automobile components, electric components, mechanical components and building components.
However, since the impact strength and the dimensional accuracy can not be said satisfactory in polybutylene terephthalate resin by itself, it has been known to blend a polybutylene terephthalate resin with a polycarbonate resin as one of countermeasures to the problem.
A thermoplastic resin composition formed by blending the thermoplastic polyester resin and the polycarbonate resin is provided with such characteristics as impact resistance, heat resistance and chemical resistance, as well as improved surface appearance and the welding strength of the molding product by further blending a methacrylate resin and an alkyl acrylate/alkyl methacrylate copolymer as described in, for example, Japanese Patent Laid-Open No. 298422/1998.
Further, Japanese Patent Laid-Open No. 2000-291973 discloses a resin composition formed by blending a polycarbonate resin and a polyester resin for which production process and kind are specified. According to the Publication, it is described that the resin composition possesses inherent characteristics such as chemical resistance of both of the resins and is also excellent in the resistance to wet heat fatigue.
Japanese Patent Laid-Open No. 291204/1997 describes a resin composition formed by blending a polyester copolymer obtained from a dicarboxylic acid mainly comprises terephthalic acid and 1,4-butanediol, with polycarbonate resin, nuclear agent, inorganic filler and coloring ingredient. It is described that the composition has high mechanical strength and rigidity, as well as enhanced appearance of the molding product.
By the way, some molding products of thermoplastic polyester resin compositions are used under circumstances liable to undergo external effects such as some of car electronic components and cement-buried components. One of possibly significant problems for such molding products can include contact with rain fall or snow melt, which is rendered alkaline by some or other reasons or contact with those which are alkaline by nature such as cement. That is, when a thermoplastic polyester resin is kept in contact with an alkaline solution, it results in a problem that the mechanical strength is greatly deteriorated. Further, in a molding product formed by insert molding of a metal involves a problem that cracks are formed due to the difference in the linear expansion coefficient between the inserted metal and the resin reduced with the mechanical strength with the change of the environmental temperature. Particularly, the strength during immersion in the alkaline solution is remarkable in fibrous reinforcing material-containing products and, although they are reinforced with fibrous reinforcing material, the strength is sometimes lowered more than in the case of non-reinforced products not containing fibrous reinforcing materials.
The present inventors have made an earnest study for improving the resistance to an alkaline solution (hereinafter referred to as an alkali resistance) of a thermoplastic resin composition containing a fibrous reinforcing material and, as a result, have found that a composition comprising a polybutylene terephthalate resin containing polybutylene terephthalate/isophthalate copolymer, a polycarbonate resin, an elastomer and a fibrous reinforcing material is excellent, particularly, in view of the alkali resistance and have accomplished this invention to be described specifically later.
When this invention is compared with that in known literatures described above, it has been found that the combination of the polyester copolymer with the polycarbonate resin and the inorganic filler as described in the examples of Japanese Patent Laid-Open No. 291204/1997 can not suppress the occurrence of cracks due to the difference in the linear expansion coefficient between the inserted metal and the resin since the elastomer is not added.
On the other hand, while Japanese Patent Laid-Open No. 2000-119492 and 298422/1998 describe combinations of the polyester resin with the polycarbonate resin, inorganic filler and elastomer, what are disclosed specifically are combination of polybutylene terephthalate resin, polycarbonate resin, inorganic filler and elastomer, or a combination using a polyethylene terephthalate resin instead of the polybutylene terephthalate resin. In this case, although the ratio of an amorphous portion is large in average for the entire resin, since polyester resin itself is present locally, it can not prevent the lowering of the reinforcing effect by the fibrous reinforcing material.
This invention intends to provide a polyester resin composition excellent in an alkali resistance and also excellent in a mechanical strength, as well as an insert molding product using the composition.
For solving the subject described above, the invention comprises the following constitution:
1. A polyester resin composition comprising
(A) 30 to 95 parts by weight of a polybutylene terephthalate resin containing a polybutylene terephthalate-isophthalate copolymer in which the content of an isophthalic acid ingredient to the entire dicarboxylic acid ingredient is 3 to 30 mol %,
(B) 1 to 30 parts by weight of a polycarbonate resin,
(C) 1 to 30 parts by weight of an elastomer and
(D) 3 to 60 parts by weight of a fibrous reinforcing material, wherein the total amount for (A)-(D) is 100 parts by weight.
2. A polyester resin composition as defined in (1) above, wherein (E) 0.1 to 5 parts by weight of a silicone compound is added and blended based on 100 parts by weight of the total amount for (A)-(D).
3. A polyester resin composition as defined in (2) above, wherein the silicone compound (E) is a dimethyl silicone oil having a viscosity as measured at 25xc2x0 C. of 10,000 mm2/s or less and containing 1,000 ppm or less of a low molecular weight siloxane with a molecular weight of 800 or less.
4. A polyester resin composition as defined in any one of (1) to (3) above, wherein the elastomer (C) is an ethylenic copolymer formed by copolymerizing ethylene with one or more of an xcex1-olefin of 3 or more carbon atoms, an xcex1,xcex2 unsaturated acid and an alkyl ester thereof.
5. A polyester resin composition as defined in any one of (1) to (4) above, wherein the fibrous reinforcing material (D) is one of glass fiber and wollastonite.
6. A polyester resin composition as defined in any one of (1) to (5) above, which is used for insert molding.
7. An insert molding product comprising the polyester resin composition as defined in any one of (1) to (5) above.
As described above, since the polyester resin composition contains specified polybutylene terephthalate resin, polycarbonate resin, elastomer and fibrous reinforcing material each at a specified ratio, a polyester resin composition excellent in resistance to alkaline solutions and also excellent in mechanical strength can be obtained.
Further, an insert molding product excellent in alkali resistance and mechanical strength can be obtained from the polyester resin composition by insert molding of a metal.